For introducing a 7.beta.-hydroxyl group into a 7-unsubstituted bile acid utilizing the conversion by a microorganism, the following methods have been known:
1) A process for preparing 3.alpha., 7.beta., 12.alpha.-trihydroxy-5.beta.-cholanic acid (hereinafter, referred to as ursocholic acid) from 3.alpha., 12.alpha.-dihydroxy-5.beta.-cholanic acid (hereinafter, referred to as deoxycholic acid) using one or more microorganisms belonging to the genus Pleurotus, the genus Coriolus, the genus Daedaleopsis, the genus Panaeolus, the genus Marasmius, the genus Crinipellis, the genus Pholiota or the genus Fusarium. (Japanese Patent Publication No. 34038 of 1989)
2) A process for preparing ursodeoxycholic acid from 3.alpha.-hydroxy-5.beta.-cholanic acid (hereinafter, referred to as lithocholic acid) using a microorganism belonging to the genus Fusarium. (Japanese Patent Publication No. 29397 of 1991)
3) A process for preparing a conjugated form of ursodeoxycholic acid from a conjugated form of lithocholic acid using a microorganism belonging to the genus Mortierella. (Japanese Patent Publication No. 29438 of 1993)
When a 7.beta.-hydroxyl group was introduced using these microorganisms, however, it was necessary to adjust the concentration of a substrate at a level as low as approximately 0.02-0.1% v/w. Therefore, a great technical problem arose that a colossal apparatus for production was required when production at an industrial scale was carried out.
On the other hand, microorganisms of the genus Penicillium have been known having a bile acid-converting capacity by introducing a 1.beta.-hydroxyl group and a 15.beta.-hydroxyl group (Journal of Lipid Research, Vol. 22, p. 1225 (1981) ); no microorganism of the genus Penicillium, however, has been known to have a bile acid-converting capacity by introducing a 7.beta.-hydroxyl group.